Resin sheet, process and apparatus for producing same, surface light source element and laminate

ABSTRACT

A resin sheet having laminated transparent resin layers and a smooth outer surface, the refractive indexes of two resins of any adjacent two resin layers differing from each other, the interfaces among the resin layers having an uneven shape, is produced with an extrusion molding apparatus having such a structure that a plurality of transparent resins are extruded from respective separate flow passages into a composite resin flow passage to form a composite resin flow having a laminate structure with an uneven shape at the interfaces of the resin layers, and that the composite resin flow is extruded from an outlet of the composite resin flow passage. The resin sheet is used as a laminate, or a light guide of a surface light source element.

This is a division of application Ser. No. 08/981,170, filed Mar. 17,1998, now abandoned, which is a 371 of PCT/JP96/01319 filed May 17,1996, both of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to such a resin sheet applicable tovarious objects and uses as a light diffusing sheet and a light-guidingsheet suitable for an illuminator cover, a lighting window, a buildingmaterial, a traffic sign, a sign board, a liquid crystal display device,etc., and an artistic design sheet having a deep appearance and/or athree-dimensional appearance, and an apparatus and a process forproducing the resin sheet. Furthermore, the present invention relates toa surface light source element in which the resin sheet is used as alight guide, and a laminate in which such resin sheets are stacked.

BACKGROUND ART

Transparent resin sheets having a surface unevenness formed by a mold,transparent resin sheets coated with a light-diffusing agent orlight-scattering agent on the back surface, and similar resin sheets,have been known as light diffusible resin sheets.

Transparent resin sheets subjected to shading printing, shadow printing,or the like printing, and transparent resin sheets having an unevennessin the interior have been known as artistic design sheets.

Japanese Examined Utility Model Publication (Kokoku) No. 7-36742discloses a luminous decorative sheet prepared by successivelylaminating a transparent resin layer, a transparent embossed resin layerand a light reflective layer. However, the light reflective layer islaminated to the portion having an uneven pattern in the transparentembossed resin layer. As a result, the sheet is not suited to a lightguide which is used by making light incident on the back surface or sideof the sheet.

Japanese Unexamined Patent Publication (Kokai) No. 3-256735 discloses acut-glass-like sheet which is a composite sheet prepared by formingV-shaped grooves on one side of a polyvinyl chloride sheet, and bondinga polyvinyl chloride sheet having a smooth surface to the V-shapedgroove-formed surface and which has a closed air layer in the V-shapedgroove portion. However, since such a sheet having a structure with aninner air layer shows a large difference in refractive indexes betweenthe resin layer and the air layer, the light divisibility becomes toolarge. The sheet is, therefore, not suitable for a light guide.

On the other hand, as an instance of a back surface light source deviceused for a liquid crystal display device, a sign board, a traffic sign,etc., there is an edge-lit-type back surface light source device inwhich a linear light source is arranged on an end surface of aplate-like light guide. Such an edge-lit-type back surface light sourcedevice is one wherein a plate-like transparent material such as anacrylic resin plate is used as a light guide, light from a light sourcearranged on one side end thereof is made incident thereon, and light isallowed to exit in a plane form from the surface (light-exiting surface)thereof. The light guide used herein usually has a light-scatteringportion and/or light-diffusing portion formed on the surface or on theback surface. Such a surface light source element is required to ensurethe uniformity of the luminance of the exiting light regardless of thedistance from the light source. The performance is particularlyimportant to a large size surface light source element.

Japanese Unexamined Patent Publication (Kokai) No. 5-127159 discloses asurface light source element having a light guide the surface of whichis printed with a light-diffusing material such as titanium white in adot form, and a prism sheet is placed on the light-exiting surface.uniform luminance can be obtained from such a surface light sourceelement by changing the covering ratio of the dots according to adistance from the light source. However, the dot-like pattern must beshielded with a light diffusible sheet. Consequently, the luminance islowered, and the structure of the surface light source element becomescomplicated.

Japanese Unexamined Patent Publication (Kokai) No. 2-84618 discloses asurface light source element having a light guide with a satin surfaceat least on one of the surface (light-exiting surface) and the backsurface, and a prism sheet placed on the light-exiting surface. Althougha very high luminance can be obtained from such a surface light sourceelement, the uniformity of the luminance of the exiting light is notsatisfactory.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a transparent resinsheet which can be used as a light guide, a light diffusible sheet, anartistic design sheet, etc.

Another object of the present invention is to provide an apparatus and amethod capable of producing the resin sheet at low cost with highproductivity.

A further object of the present invention is to provide a surface lightsource element in which the resin sheet is used as a light guide.

A still further object of the present invention is to provide a resinsheet laminate in which the resin sheets are laminated.

The above-mentioned objects of the present invention can be achieved bythe present invention having the constitutions as described below.

1. A resin sheet having a laminate structure in which a transparentresin layer C is sandwiched between a transparent resin layer A and atransparent resin layer B, and having a smooth outer surface, any twoadjacent resin layers of the three resin layers having refractiveindexes which differ from each other,

in a cross-section represented by an xy plane wherein y is a thicknessdirection of the resin sheet, and x is a width direction thereof, atleast one of two interfaces formed between the resin layers A and C andbetween the resin layers B and C having an uneven shape.

2. A resin sheet having a laminate structure of a transparent resinlayer A and a transparent resin layer B, and having a smooth outersurface,

the adjacent resin layers having refractive indexes which differ fromeach other,

in a cross-section represented by an xy plane wherein y is a thicknessdirection of the resin sheet, and x is a width direction thereof, aninterface formed between the resin layers A and B having an unevenshape.

3. An apparatus for producing the resin sheet in 1 above which comprises

a composite resin flow passage 21 having a predetermined width in the Xdirection, a predetermined thickness in the Y direction and apredetermined length in the Z direction, and comprising a composite flowformation portion 22 at one end in the Z direction, and a composite flowoutlet 23 at the other end,

a slit-like flow passage 31 extending in the X direction, for allowing aresin c for the resin layer C to flow toward the Z direction in thecomposite flow formation portion 22, and

two flow passages 41, 42 for allowing a resin a for the resin layer Aand a resin b for the resin layer B to flow into the composite flowformation portion 22 from both sides of an XZ plane including the flowpassage 31 for the resin c,

at least one of the XZ cross-sections of the flow passages 41, 42 forthe respective resins a and b having a shape in which a portion orportions (Ln and/or Rn) having a large height in the Z direction and aportion or portions (Lm and/or Rm) having a small height (includingzero) in the Z direction are alternately arranged.

4. An apparatus for producing the resin sheet in 2 above which comprises

a composite resin flow passage 21 having a predetermined width in the Xdirection, a predetermined thickness in the Y direction and apredetermined length in the Z direction, and comprising a composite flowformation portion 22 at one end in the Z direction, and a composite flowoutlet 23 at the other end, and

two flow passages 41, 42 for allowing a resin a for the resin layer Aand a resin b for the resin layer B to flow into the composite flowformation portion 22 from both sides of an XZ plane including the flowpassage 21,

at least one of XZ cross-sections of the flow passages 41, 42 for therespective resins a and b having a shape in which a portion or portions(Ln and/or Rn) having a large height in the Z direction and a portion orportions (Lm and/or Rm) having a small height (including zero) in the Zdirection are alternately arranged.

5. A process for producing a resin sheet with the apparatus in 3 abovecomprising

allowing the resin c for the transparent resin layer C to flow into thecomposite flow formation portion 22 through the slit-like flow passage31,

allowing, on the other hand, the resin a for the transparent resin layerA and the resin b for the transparent reins layer B to flow into thecomposite flow formation portion 22 through the two respective flowpassages 41, 42 so that a cross-sectional shape of a molten resin layerformed from the resin c is deformed by flow action of the resins a andb, and

taking off a resin sheet flowing out from the composite flow outlet 23.

6. A process for producing a resin sheet with the apparatus in 4 abovecomprising

allowing the resin a for the transparent resin layer A and the resin bfor the transparent resin layer B to flow into the composite flowformation portion 22 through the two respective flow passages 41, 42 sothat a cross-sectional shape of a bonded portion of the resins a and bis deformed by flow action of the resins a and b, and

taking off a resin sheet flowing out from the composite flow outlet 23.

7. A surface light source element comprising the resin sheets in 1 or 2above as a light guide 51,

a reflective material 52 arranged on the back surface of the lightguide,

a light source 53 placed on at least one end surface (yz plane) in the xdirection of the light guide, and

a light-deflecting sheet 54 placed on a surface thereof and having afunction of changing the direction of the light which is allowed to exitfrom the surface thereof to the normal direction thereof.

8. A resin sheet laminate comprising at least two resin sheets in 1 or 2above, the x directions of any two adjacent resin sheets being deviatedfrom each other at a predetermined angle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic plan view of an embodiment of the apparatusaccording to a first aspect of the present invention.

FIG. 2 is a schematic side view of the apparatus in FIG. 1.

FIG. 3 is a schematic plan cross-sectional view schematically showing anembodiment of the internal structure of the apparatus in FIG. 1.

FIG. 4 is a fragmentary cross-sectional view along the line I—I in FIG.3.

FIG. 5 is a perspective view from the direction of the line II—II inFIG. 4.

FIG. 6 is a schematic cross-sectional view for illustrating anembodiment of resin flow passages in the apparatus in FIG. 1.

FIG. 7 is a fragmentary cross-sectional view along the line IV—IV inFIG. 6.

FIG. 8 is a schematic view showing the cross-sectional shape of theresin layers formed in the composite resin flow passage shown in FIG. 6.

FIG. 9 is a schematic cross-sectional view for illustrating anotherembodiment of resin flow passages in the apparatus in FIG. 1.

FIG. 10 is a schematic view showing the cross-sectional shape of theresin layers formed in the composite resin flow passage in FIG. 9.

FIG. 11 is a schematic cross-sectional view for illustrating stillanother embodiment of resin flow passages in the apparatus in FIG. 1.

FIG. 12 is a schematic view showing the cross-sectional shape of theresin layers formed in the composite resin flow passage in FIG. 11.

FIG. 13 is a schematic cross-sectional view showing another embodimentof the cross-sectional shape of the resin layers formed in the compositeresin flow passage in the apparatus in FIG. 1.

FIG. 14 is a schematic cross-sectional view showing the shape of theresin flow passages in FIG. 13.

FIG. 15 is a schematic cross-sectional view showing still anotherembodiment of the cross-sectional shape of the resin layers formed inthe composite resin flow passage in the apparatus in FIG. 1.

FIGS. 16a to 16 f are schematic cross-sectional views each showinganother embodiment of the resin flow passages as shown in FIG. 14.

FIG. 17 is a schematic cross-sectional view showing still anotherembodiment of the resin flow passages in the apparatus in FIG. 1.

FIG. 18 is a schematic plan cross-sectional view showing anotherembodiment of the construction of the apparatus according to the presentinvention.

FIG. 19a is a schematic plan cross-sectional view showing the dieportion of the apparatus in FIG. 18, and

FIG. 19b is a corresponding side cross-sectional view of the die portionin FIG. 19a.

FIG. 20 is a schematic plan cross-sectional view showing an embodimentof the internal structure of the apparatus according to a second aspectof the present invention.

FIG. 21 is a schematic cross-sectional view showing an embodiment of theresin flow passages in the apparatus in FIG. 20.

FIG. 22 is a schematic view showing the cross-sectional shape of theresin layers formed in the composite resin flow passage in FIG. 21.

FIG. 23 is a schematic cross-sectional view showing another embodimentof the resin flow passages in the apparatus in FIG. 20.

FIG. 24 is a schematic view showing the cross-sectional shape of theresin layers formed in the composite resin flow passage in FIG. 23.

FIG. 25 is a schematic cross-sectional view showing another embodimentof the resin flow passages in the apparatus in FIG. 20.

FIG. 26 is a schematic view showing the cross-sectional shape of theresin layers formed in the composite resin flow passage in FIG. 25.

FIG. 27 is a schematic view showing the cross-sectional shape of theresin layers formed in the composite resin flow passage when resin flowpassages having another shape is used in FIG. 21.

FIG. 28 is a schematic cross-sectional view showing still anotherembodiment of the resin flow passages in the apparatus in FIG. 1.

FIGS. 29a to 29 i are cross-sectional views each showing anotherembodiment of the structure of a resin sheet obtained by the apparatusof the present invention.

FIGS. 30a to 30 k are cross-sectional views each showing anotherembodiment of the structure of a resin sheet obtained by the apparatusof the present invention.

FIGS. 31a to 31 h are cross-sectional views each showing anotherembodiment of the structure of a resin sheet obtained by the apparatusof the present invention.

FIG. 32 is a schematic view showing an embodiment of a surface lightsource element of the present invention.

FIG. 33 is a schematic view for illustrating a method for evaluating thesurface light source element in examples.

FIG. 34 is a cross-sectional view showing the structure of a resin sheetobtained in Comparative Example and internally having an air layer.

BEST MODE FOR CARRYING OUT THE INVENTION

The apparatus for producing a resin sheet, the process for producing thesame, the resin sheet, the surface light source element and the resinsheet laminate according to the present invention will be successivelyexplained hereinafter.

In the apparatus (apparatus disclosed in claim 7) according to a firstaspect of the present invention, the X, Y and Z directions agree withthe width direction, the thickness direction and the running directionof the resin sheet, respectively. The Z direction may be made to agreewith the vertical direction as shown in FIG. 4, or with the horizontaldirection as shown in FIG. 2.

The significant features of the apparatus according o the first aspectof the present invention are the shape and arrangement of the two flowpassages 41 and/or 42 for allowing the resin a for the resin layer A andthe resin b for the resin layer B to flow into the composite flowformation portion 22 (FIG. 4). That is, the shapes of the flow passages41 and/or 42 in the XZ cross-section are characterized in that a portionor portions Rn and/or Ln each having a large height in the Z directionand a portion or portions Rm and/or Lm each having a small height (caseswhere the heights are 0 being allowed) are alternately arranged (FIG.6).

FIG. 1 shows an apparatus employed when the resin a for forming theresin layer A is the same as the resin b for forming the resin layer B.The resin is termed a resin a (or b). The resin a (or b) is melted andextruded by a first extruder 1 into a molding head and reaches a firstvolume regulating pump 3 through a first flow passage 11. The resin cfor forming the resin layer C is melted and extruded by a secondextruder 2 into the same molding head and reaches a secondvolume-regulating pump 4 through a second flow passage 12. The resin a(or b) is distributed to two flow passages 13, 16 arranged on the leftand right sides, respectively through a distributing nozzle providedwithin a die pack 5, to form resin flows of the resin a and the resin b(FIG. 3). Moreover, the resin c is introduced into the flow passage 31by the distribution nozzle through a flow passage 14 provided within thedie pack 5 (FIG. 4).

In addition, when the resin a differs from the resin b, one of the tworesins is supplied by a third extruder (not shown).

The resin c is discharged into the composite flow formation portion 22from the slit-like flow passage 31 to form a sheet-like flow having apredetermined thickness (FIG. 4). On the other hand, the resins a and bare allowed to flow so that the resin c, discharged into the compositeflow formation portion 22, is sandwiched therebetween to form acomposite resin flow. The composite resin is extruded from the compositeflow outlet 23, and taken off by cooling rolls 10 to have a sheet-likeform. The sheet-like material is cut in predetermined lengths by a sheetcutter 15 (FIGS. 1, 2). In addition, when the composite resin is to beshaped into a thin film-like material, the discharged resin is coiled bya coiler after passing through cooling rolls.

In the composite flow formation portion 22, the resins a and b exertaction on the resin c depending on the relative arrangement of the flowpassages 41, 42 and the flow passage 31, and the resin c is consequentlydeformed to have a desired cross-sectional shape in the XYcross-section.

The apparatus and the process for producing the resin sheet of thepresent invention will be explained below with reference to thedrawings.

FIGS. 1 to 4 are schematic views showing one embodiment of the apparatusaccording to the first aspect of the present invention. FIGS. 1 and 2are a schematic plan view and a schematic side view of the entireapparatus, respectively. FIGS. 3 and 4 are a plan cross-sectional viewand a vertical cross-sectional view, respectively showing an embodimentof the inner structure of the apparatus.

FIG. 5 is a perspective view from the direction of the line II—II inFIG. 4.

FIGS. 6 and 7 show resin flow passages in a production apparatus whichis a typical embodiment of the present invention. FIG. 6 is afragmentary cross-sectional view along the line III—III shown in FIG. 4.

FIG. 7 is a fragmentary cross-sectional view along the line IV—IV inFIG. 6.

In the apparatus, the flow passage 31 has an outlet having a constantspacing from one end in the X direction of the composite flow formationportion 22 to the other end.

Portions Ln, Lm of the flow passages 41 and portions Rn, Rm of the flowpassages 42 are symmetrically arranged with respect to the XZ planeincluding the flow passage 31. The width of the portions Ln and that ofthe portions Rn in the X direction are equal, and the width of theportions Lm and that of the portions Rm are also equal. The height ΔLnand the height ΔRn in the Z direction are equal, and the height ΔLm andthe height ΔRm are also equal. The widths and heights of the portionsLn, Lm and the portions Rn, Rm may be suitably varied from one apparatusto another one, or within the same apparatus. The flow amounts and flowrates of the resins a and b are determined by the widths and heights ofthese flow passages.

FIG. 8 shows the cross-sectional shape of the resin layer at thedownstream site of the composite resin flow passage in FIG. 6. The resinc allowed to flow out from the flow passage 31 in a flat plate form isdeformed by the flow action exerted by the resins a and b shown byarrows in FIG. 6. As a result, the cross-sectional shape of the resinlayer C comes to have a structure in which lens-shaped blocks areconnected as shown in FIG. 8 and FIG. 30a. In addition, in FIG. 8, inorder to easily understand the relationship between the shapes of theflow passages 41, 42 and the cross-sectional shape of the resin sheetfinally produced, the flow passages 41, 42 situated upstream comparedwith the position of the figure are also shown in the same figure, forconvenience.

FIGS. 9 and 10 are schematic views showing another embodiment of theapparatus according to the first aspect of the present invention. FIG. 9is a fragmentary cross-sectional view along the line III—III in FIG. 4.FIG. 9 shows an apparatus in which the portions Ln, Lm are formed in theflow passages 41, and in which neither the portions Rn nor the portionsRm is formed in the other flow passages 42. The cross-sectional shape ofthe flow passages 41 is the same as in FIG. 7. FIG. 10 is a syntheticfigure represented in the same manner as in FIG. 8.

When such an apparatus is used, a resin sheet, having uneven depressionsand protrusions on the side of the interface between the resin layer Aand the resin layer C as shown in FIGS. 10 and 29b, is produced.

FIGS. 11 and 12 are schematic views showing another embodiment of theapparatus according to the first aspect of the present invention. FIG.11 is a fragmentary cross-sectional view along the line III—III in FIG.4. In the apparatus in FIG. 11, the portions Ln of the flow passages 41and the portions Rm of the flow passages 42 are symmetrically arrangedwith respect to the XZ plane including the flow passage 31, and theportions Lm of the flow passages 41 and the portions Rn of the flowpassages 42 are symmetrically arranged with respect thereto. Thecross-sectional shapes of the flow passages 41, 42 are the same as inFIG. 7. FIG. 12 is a synthetic figure represented in the same manner asin FIG. 8.

When the apparatus is used, a resin sheet as shown in FIG. 12 or FIG.30d is produced.

The arrangement of the portions Ln, etc. of the flow passages 41, 42 inFIG. 13 is the same as in FIG. 6, and FIG. 13 shows an apparatus havinga structure in which small amounts of the resins a and b can flowthrough the portions Lm, Rm each having a small flow passage height asshown in FIG. 14. FIG. 13 is also a synthetic view represented in thesame manner as in FIG. 8.

When the apparatus is employed, a resin sheet as shown in FIG. 13 orFIG. 30b is produced.

FIG. 15 shows an apparatus in which the flow passages 41, in FIG. 6 aretilted at a predetermined angle of φ to the YZ plane. FIG. 15 is also asynthetic view represented in the same manner as in FIG. 8. A resinsheet as shown in FIG. 15 or FIG. 30c is produced by the use of theapparatus.

Typical embodiments of the apparatus according to the first aspect ofthe present invention have been explained above. As the shapes of theflow passages 41, 42 corresponding to FIG. 7 and FIG. 14, various shapesas shown in FIGS. 16a to 16 f can be adopted. The pitch p and the heighth of the uneven shape of these depressions and protrusions are suitablyvaried.

Moreover, as shown in FIG. 17, the flow passages 41, 42 flowing towardthe composite flow formation portion 22 can also be tilted at apredetermined angle of θ to the XZ plane.

The outlet of the flow passage 21 can have various structures inaccordance with the object. For example, as shown in FIG. 18 and FIGS.19a and 19 b, the spacing of the cross-section of a flow passage (XYcross-section) in the X direction and the spacing thereof in the Ydirection can be narrowed toward the flow passage outlet 45 by attachinga die 44. Use of such a structure promotes the forming the uneven shapeof depressions and protrusions at the interface of the resins.

Furthermore, the outlet of the flow passage 31 can also be offset fromthe central position between the flow passages 41, 42 shown in FIG. 4 toone of them.

FIG. 20 is a schematic plan cross-sectional view showing an embodimentof the internal structure of the apparatus according to a second aspectof the present invention. The apparatus differs from the apparatus (FIG.3) according to the first aspect of the present invention in that it hasno flow passage for the resin c. The apparatus is fundamentally the sameas the apparatus according to the first aspect of the invention exceptfor the aspect mentioned above.

That is, the apparatus has the same composite resin flow passage 21 andthe same flow passages 41, 42 as in the apparatus according to the firstaspect of the invention. The arrangement, the sizes and the shapes ofthe portions Ln, Lm of the flow passages 41 and those of the portionsRn, Rm of the flow passages 42 can be employed variously in the samemanner as in the apparatus according to the first aspect of theinvention.

In the apparatus in FIG. 21, the portions Ln of the flow passages 41 andthe portions Rm of the flow passages 42 are symmetrically arranged withrespect to the XZ plane passing through the central portion of thecomposite flow formation portion 22, and the portions Lm of the flowpassages 41 and the portions Rn of the flow passages 41 aresymmetrically arranged with respect to the same XZ plane. Thecross-sectional shapes of flow passages 41, 42 are the same as those inFIG. 7. When the apparatus is used, a resin sheet having the interfaceof both resin layers in a polygonal line form in the XY cross-section isproduced, as shown in FIG. 22. In addition, FIG. 22 is a synthetic viewrepresented in the same manner as in FIG. 8.

When an apparatus, wherein the portions Rn, Rm are formed in the flowpassages 42 and a flow passage having a constant height is formed overthe entire flow passage 41 in the x direction as shown in FIG. 23, isused a resin sheet in which the interface is offset to the rein layer Bas shown in FIG. 24 or 31 c is produced. FIG. 24 is a synthetic viewrepresented in the same manner as in FIG. 8.

The apparatus in FIG. 25 is one in which the positional relationshipbetween the portions Ln of the flow passages 41 and the portions Rn ofthe flow passages 42 is shifted to some degree compared with therelationship in the apparatus in FIG. 21. A resin sheet as shown in FIG.26 or FIG. 31e is produced when the apparatus is used. FIG. 26 is asynthetic view represented in the same manner as in FIG. 8.

When the cross-sectional shapes of the flow passages 41, 42 in theapparatus of FIG. 21 are altered to those shown in FIG. 14, the resins aand b flow through the portions Rm, Lm each having a small passageheight, in small amounts. Consequently, a resin sheet as shown in FIG.27 or FIG. 31a is produced. FIG. 27 is a synthetic view represented inthe same manner as in FIG. 8.

The directions of the flow passages 41, 42 can be tilted at apredetermined angle φ with respect to the YZ plane as shown in FIG. 28,in the same manner as in FIG. 15. As a result, a resin sheet as shown inFIG. 31e is similarly obtained.

Furthermore, the flow passages 41, 42 flowing toward the composite flowformation portion 22 can be tilted at a predetermined angle of θ to theXZ plane in the same manner as in FIG. 17.

A wide range of thermoplastic resins may be used as the resins in thepresent invention. There is no specific limitation on the resins a, band c for the resin layers A, B and C so long as the resins aretransparent. Examples of the resins include polyethylene terephthalate,polyvinyl chloride, polystyrene, polycarbonate, various acrylic resinsrepresented by polymethyl methacrylate, amorphous polyolefins,polyamides, polymethylpentene, copolymer or blend resins of thesepolymers, acrylonitrile/styrene copolymer and methylmethacrylate/styrene copolymer. When transparency, weatheringresistance, etc. are specifically required, acrylic resins arepreferred, and polymethyl methacrylate is particularly preferred.

The combination of the resins a, b and c are suitably selected inaccordance with the object. When the light divisibility is to beimparted to the resin sheet, a difference in the refractive indexes mustbe considered. Since adhesion among the resins influences theproductivity of the resin sheet, the adhesion thereamong must beconsidered. Moreover, it is also important to select a combination ofresins, to be laminated, in which the melting points of which differlittle.

In order to prevent warping of the resin sheet, it is preferred that theresin sheet have a three-layered structure of the resin layers A, C andB, and that the physical properties of the resins a and b for therespective resin layers A and B be the same or similar to each other,particularly the resins a and b should be of the same kind of resin orthe same resin.

Furthermore, when artistic design and a deep appearance are to beimparted to the resin sheet or when optical properties are to beimparted thereto, each of the resin layers may be colored by allowing itto contain organic or inorganic dyes or pigments, or it may be allowedto contain a light-diffusing agent, etc.

As exemplified in FIGS. 29a to 29 i, FIGS. 30a to 30 k and FIGS. 31a to31 h, the shape of the depressions and protrusions at the interfacebetween any of the two resin layers formed in the xy cross-section ofthe resin sheet may take a linear shape such as a polygonal line formand a sawtooth form, or a curved shape such as a semi-circular form, asemi-elliptical form, a wave form, a parabolic form of the n-th powerand a parabolic form of the 1/n-th power.

When light divisibility is to be imparted to the resin sheet, the lightdivisibility can be adjusted by suitably selecting the angle α betweenthe sheet surface and the interface having a shape of depressions andprotrusions shown in FIGS. 30a and 31 b in the xy cross-section of theresin sheet, and the h/p ratio. Moreover, the repeating pitch p of thedepressions and protrusions, the thickness of the resin layer C or B(namely, v or t in the figure), the entire thickness of the sheet, etc.are suitably determined in accordance with the object of impartingfunctionality. Furthermore, the repeating pitch p of the depression andprotrusion unit and the h/p ratio can be suitably changed within oneresin sheet. However, from the standpoint of maintaining the uniformityof the light divisibility, it is preferred that the pitch p be the samewithin the sheet.

Since the shape of depressions and protrusions is formed within theresin sheet of the present invention, the shape thereof suffers nodamage during use. Moreover, since the surface of the resin sheet issmooth, a decreased amount of dust, etc. adheres to the surface of theresin sheet compared with a resin sheet having depressions andprotrusions on the surface.

Furthermore, the production apparatus of the present invention iscapable of producing a resin sheet having the shape of depressions andprotrusions therewithin by one step, and achieves the significant effectof producing the resin sheet at an extremely high rate.

Next, the surface light source element of the present invention will beexplained.

Since the resin sheet of the present invention has an excellent lightdivisibility, it can be used as the light guide of a surface lightsource element.

The x, y and z directions of a resin sheet forming the surface lightsource of the surface light source element are also defined as the x, yand z directions of the surface light source element, respectively.Moreover, as to the light guide (resin sheet), the side to which areflective material 52 is applied is termed a back surface (or lowersurface) and the side to which a light-deflecting sheet 54 such asprisms is laminated is termed a surface (or upper surface) (FIG. 32) forconvenience of explanation. Accordingly, the relation of upper and lowersides does not necessarily agree with the actual relation thereof at thetime when the surface light source element is actually used.

In the surface light source element of the present invention, a lightsource 53 is arranged at least on one end surface (yz plane) in the xdirection of the light guide. In FIG. 32, the light source is placed onone end surface alone. A reflecting material is suitably applied to theother two or three end surfaces.

When a light guide is formed from at least two resin layers havingrefractive indexes different from each other and the interfaces amongthe resin layers have the shape of depressions and protrusions, lightpropagates through the light guide while being repeatedly reflected andrefracted in accordance with Snell's law at the interfaces and thesurfaces of the light guide. Of the light reaching the surface or backsurface of the light guide, the portion of light exceeding the criticalangle exits the light guide.

The present inventors have found that the relationship between theexiting intensity (I) of light at a point of the surface light sourceelement and the exiting intensity (I₀) of light at the light-incidentsurface can be expressed experimentally by the formula (1)

I=I ₀(1−Φ/100)^(L′/t)  (1)

wherein Φ is a light-exiting ratio, L′ is a distance from thelight-incident end surface, and t is a thickness of the light guide.

It can be seen from formula (1) that the uniformity of the illuminancewithin the light-exiting surface is determined by the light-exitingratio Φ when the length L and the thickness t of the light guide aredetermined.

In addition, the exiting ratio Φ of light in the light guide can beobtained by the following procedure: the luminance of the light ismeasured in the central zone in the z direction of the light guide atintervals of 20 mm from the light-incident end surface; the logarithmicvalue of the luminance is plotted against the ratio of a distance fromthe light-incident surface to the thickness (L′/t) (abscissa); the slopeK of the resultant line is derived; and Φ is obtained form the formula(2)

Φ=(1−10^(k))×100  (2)

The variation (R %) represented by the formula (3) mentioned below isused as a measure of the uniformity of the luminance distribution, andthe uniformity of the luminance distribution in the surface light sourceelement is evaluated. The variation (R %) can be obtained as describedbelow. The luminance of the light guide is measured approximately in thecentral zone in the z direction thereof, initially at the point 15 mmapart from the light-incident end surface in the x direction and then atevery point at spacings of 20 mm in the same direction to the endportion opposite to the light-incident end surface. The maximum value(I_(max)), the minimum value (I^(min)) and the average value (I_(av)) ofthe luminance are obtained from the measured luminances, and R % isdetermined from the formula (3)

R%={(I _(max) −I _(min))/I _(av)}×100  (3)

As a result, the exiting ratio Φ and the variation R % are found todepend on the length L and the thickness t of the light guide and be ina specific relation; the variation R % increases with the exiting ratioΦ, and the variation R % increases with the ratio (L/t) of a length L toa thickness t of the light guide when the exiting ratio is constant.That is, it is understood that in a light guide having a certainmagnitude, the uniformity (variation) of the luminance distributionwithin the light-exiting surface of the light guide depends on theexiting ratio Φ from the light guide, and that the uniformity of theluminance distribution can be maintained by controlling the exitingratio Φ of the light.

On the other hand, the surface light source element is required toproduce light which is incident on the light-incident end surface exitfrom the light-exiting surface with good efficiency. Accordingly, theexiting ratio of light (Φ) of the light guide must be at least a certainvalue, because the amount of light repeatedly undergoing round trippropagation increases, without exiting from the light-exiting surface,when the exiting ratio of light is too low. That is, the exiting ratioof light (Φ) of the light guide must be set at the optimum valuecorresponding to the size of the light guide while both the uniformityof the luminance distribution in each of the regions of thelight-exiting surface and the provision of high luminance are taken intoconsideration.

For a resin sheet suited to such a light guide, a difference inrefractive indexes between the adjacent resin layers is preferably from0.03 to 0.3, more preferably from 0.05 to 0.25, particularly preferablyfrom 0.05 to 0.20.

When a difference in the refractive indexes is too small, a change inthe traveling direction of light at the interface of the resins becomestoo small, and consequently the exiting ratio of light (Φ) of the lightguide becomes too small. Conversely, when a difference in the refractiveindexes is too large, a change in the traveling direction of light atthe interface of the resins becomes excessive, and the exiting ratio oflight (Φ) of the light guide becomes too large.

Examples of a preferred combination of the resins include a combinationof polycarbonate, polyethylene terephthalate, polystyrene, polyethylene,or the like with polymethyl methacrylate.

When the resin sheet of the present invention is used as the light guideof a surface light source element, the exiting ratio of light of thelight guide is influenced by the pitch p and the h/p ratio in FIGS. 30ato 30 k and FIGS. 31a to 31 h.

The h/p ratio is preferably about from 0.05 to 0.5 under the conditionsthat the difference in the refractive indexes between resins of any twoadjacent resin layers is from 0.03 to 0.3 and that both the pitch p andthe height h of the shape of the depressions and protrusions at theinterface of the resin layers in the xy cross-section are constant.

The pitch of the shape of the depressions and protrusions is desirablyup to 600 μm. Since the structure of the depressions and protrusions isvisually observed when the pitch is larger than the value mentionedabove, the resin sheet is not suitable for use in sign boards, trafficsigns, liquid crystal display devices, etc., where the appearance isregarded important. When the resin sheet is used for the surface lightsource element of a liquid crystal display device, the pitch isdesirably up to 200 μm. Although there is no specific limitation on thelower limit of the pitch of the shape of the depressions andprotrusions, the lower limit is preferably about at least 50 μm in viewof an ease of production.

When the resin sheet of the present invention is used as a light guidein an edge light type surface light source element as shown in FIG. 32,the direction in which the light intensity of light exiting from thesurface of the light guide becomes maximum is inclined from the normalof the surface (xz plane) to the x direction at an angle of at least50°. Accordingly, the direction of the exiting light must be deflectedto namely to the normal direction, the observer's position. Alight-deflecting sheet 54 is, therefore, placed on the light guide inthe surface light source element of the present invention.

Examples of the light-deflecting sheet include a light diffusing sheetand a lens sheet where many columnar lens units are arranged in such amanner, at least on one side of the sheet, that the longitudinaldirections of the lens units become parallel to each other.

Various shapes of lenses forming the lens sheet may be selected inaccordance with the object. Examples of the shape include a prism shape,a lenticular shape and a wave shape. The pitch of the lens units of thelens sheet is preferably from 30 to 500 μm. When the lens sheet isplaced, whether the lens surface is made to face the side of the lightguide or the opposite side may be determined by taking the distributionof light exiting from the light guide into consideration.

When a prism sheet is used as the lens sheet, the apex angle of theprism is suitably selected in view of the distribution of exiting lightfrom the light guide. In general, the apex angle is preferably from 50to 120°.

In the surface light source element of the present invention, aplurality of light-deflecting sheets may optionally be used. Forexample, when two lens sheets are used, the two lens sheets arelaminated so that the longitudinal direction of the columns of thecolumnar lens units in one lens sheet becomes parallel to or makes anangle with that of the columns thereof in the other lens sheet. The twolens sheets may be placed so that both of the lens surfaces face theupper side or lower side. Alternatively, the two lens sheets may beplaced so that the lens surface of one lens sheet face a directionopposite to the direction of the lens surface of the other lens sheet.

When a plurality of lens sheets are to be used as light-deflectingsheets, preferred examples of using the lens sheets will be describedbelow. Prism sheets are used as the lens sheets. A first prism sheet isplaced on the surface of the light guide so that the prism surface facesthe side of the light guide (namely, downward) and the longitudinaldirection of the columnar prism units becomes parallel to the z axis. Asecond prism sheet is placed on the first prism sheet so that the prismsurface faces the side opposite to the side of the light guide (namely,upward) and the longitudinal direction of the columnar prism unitsbecomes parallel to the x axis direction. It is desirable that the apexangle of the first prism sheet be from 50 to 70° and that the apex angleof the second prism sheet be from 80 to 100°.

When only one lens sheet is used as the light-deflecting sheet, thefollowing procedure is preferred: the prism sheet has an apex angle of50 to 70° the prism surface faces the side of the light guide; and thelongitudinal direction of the columnar lens units becomes parallel tothe z axis of the surface light source element.

Furthermore, the present invention provides a resin sheet laminatehaving at least two resin sheets of the present invention as mentionedabove which are laminated together, and in which the x direction of anyone of the resin sheets deviates from that of its adjacent resin sheetat a predetermined angle. In this case, the x directions of any adjacenttwo resin sheets can be crossed at an angle of 0 to 90°. The crossingangle (deviation angle) is particularly preferably 90°.

Dust and foreign matter adhere with difficulty to the laminate of thepresent invention. The laminate gives a sheet to which an opticalfunction such as light divisibility and adjustability of the field ofview is imparted or an artistic design sheet having a deep appearanceand/or a three-dimensional appearance.

The present invention will be further illustrated with reference to thefollowing examples. In addition, methods for evaluating surface lightsource elements are as described below.

1. Measurement of Normal Luminance (1) Small Surface Light SourceElement

As shown in FIG. 33, a central zone of 20 mm wide in the z direction ofthe light-exiting surface of a surface light source element 55 isdetermined to be a measurement region. A rectangular zone of 5 mm widein the x direction from a light incident surface is excluded from themeasurement region, and the measurement region is divided into squareregions (each region: 20×20 mm) which are termed Region i, Region ii,Region iii, - - - - Region n.

A cold-cathode tube 53 (KC130T4E, 4 mm in diameter and 130 mm long,manufactured by Matsushita Electric Industrial Co., Ltd.) placed on oneend face (yz face) in the x direction of a light guide is connected to adirect voltage source through an inverter (CXA-M10L, manufactured by TDKCorporation), and lit by applying a DC voltage of 12 V.

The surface light source element is placed on a measuring table. Theoptical axis of a luminance meter 56 (nt−1°, manufactured by MinoltaCo., Ltd.) is made to coincide with a normal to the xz plane passingthrough the central position of Region i. The luminance meter is thenmoved away from the surface light source element so that the measuringdiameter becomes from 8 to 9 mm in diameter, and the luminance meter isfixed. The normal luminance of Region i is then measured, and termed Gi.

The surface light source element is then moved by 20 mm in the xdirection, and the normal luminance of Region ii is measured in the samemanner. The measured value is termed Gii. The normal luminance of theentire region is measured by repeating the operation.

(2) Large Surface Light Source Element

Measurements are made in the same manner as in (1) above (Small SurfaceLight Source Element) except that a fluorescent lamp (30 W) is used as alight source.

2. Exiting Ratio of Light

The logarithmic value of the normal luminance (log Gi, - - - - or logGn, axis of ordinates) is plotted against the corresponding ratio of adistance from the central position of the measurement region to thelight-incident end of the light guide to the thickness thereof (L′/t).The slope (K) of the straight line obtained by plotting is determined,and the exiting ratio of light (Φ) is derived from the formula (2).

3. Variation (R %)

Of Gi to Gn measured in 1 above, the maximum value, the minimum valueand the average value are termed I_(max), I_(min) and I_(av),respectively, and R % is obtained from formula (3).

EXAMPLE 1

A polymethyl methacrylate (trade name of Acrypet MD, manufactured byMitsubishi Rayon Co., Ltd.) was prepared as a resin a and a resin b, anda polycarbonate (trade name of Yupiron H-3000, manufactured byMitsubishi Gas Chemical Co., Ltd.) was prepared as a resin c. Anapparatus shown in FIGS. 1 to 5 was used. A die 8 having a slit gap of1.7 mm at the outlet of a flow passage 31 was used for the resin c. Adie 9 having the structure of a composite flow formation portion asshown in FIGS. 6 and 7 was used. The groove portions ΔRn and ΔLn wereeach set at 1 mm, and the pitch p of the groove portions was set at 5mm. The widths of the portions Ln and Rn were each set at 2.5 mm (P/2).

The molding temperature was 260° C. The polycarbonate was melted in afirst extruder 1, fed to the die 9 via an extrusion flow passage 13, andallowed to flow into a composite flow formation portion 22 from the flowpassage 31. The polymethyl methacrylate was melted in a second extruder2, fed to the die 8 via an extrusion flow passage 14, and allowed toflow into the composite flow formation portion 22 from flow passages 41,42. A composite resin flow passage 21 had a width (X direction) of 50 cmand a thickness (Y direction) of 5 mm. Both resins joined together inthe composite flow formation portion to form a composite resin flow,which was extruded from a composite resin flow outlet 23 to give acomposite sheet having a thickness of 5 mm and a width of 50 cm.

The sheet thus obtained had a smooth surface as a whole, no warpage, anda cross-section as shown in FIG. 30a. The depressions and protrusionshad a pitch of 5 mm, and an h/p ratio of 0.25. The sheet was excellentin both the appearance and the light transmittance, showed no unevenlight diffusion, and was suited for use as a light diffusing plate, andthe like.

EXAMPLE 2

A composite resin sheet having a thickness of 5 mm and a width of 50 cmwas continuously molded in the same manner as in Example 1 except that adie 9 having the structure of a composite flow formation portion shownin FIG. 11 was used, and that the height of the flow passages 41 was setat 1 mm.

The sheet thus obtained had a smooth surface as a whole, no warpage, anda cross-sectional shape of the resin layer C as shown in FIG. 30d. Thedepressions and protrusions had a pitch of 5 mm, and an h/p ratio of0.25. The sheet was excellent in both appearance and lighttransmittance, showed no uneven light diffusion, and was suited for usein a light illuminator cover and the like.

EXAMPLE 3

A composite resin sheet having a thickness of 3 mm and a width of 50 cmwas continuously molded in the same manner as in Example 1 except in thefollowing respects: the slit gap of the outlet of the flow passage 31was set at 3 mm; the pitch p of the groove portions of the flow passages41, 42 was set at 1.5 mm; and the width of the portions Ln and Rn wasset at 0.75 mm (P/2).

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape of the resin layer C as shown in FIG. 30a. Thedepressions and protrusions had a pitch of 1.5 mm, and an h/p ratio of0.25. The sheet was excellent in both appearance and lighttransmittance, showed no uneven light diffusion, and was suited for usein a light diffusing plate and the like.

EXAMPLE 4

A composite resin sheet having a thickness of 3 mm and a width of 50 cmwas continuously molded in the same manner as in Example 1 except thatthe flow passage set so that it made an angle Φ of 60° with the YZplane.

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape of the resin layer C as shown in FIG. 30c. Thedepressions and protrusions had a pitch of 5 mm, and an h/p ratio of0.25. The sheet was excellent in both appearance and lighttransmittance.

EXAMPLE 5

A composite resin sheet having a thickness of 5 mm and a width of 50 cmwas continuously molded in the same manner as in Example 1 except that adie 9, having a structure wherein the portions Ln of the flow passages41 and the portions Rm of the flow passages 42 were symmetricallyarranged with respect to the XZ plane including the flow passage 31, andthe portions Lm of the flow passages 41 and the portions Rn of the flowpassages 42 were symmetrically arranged with respect thereto, was used.

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape of the resin layer C as shown in FIG. 29f. Thedepressions and protrusions had a pitch of 5 mm. The sheet was excellentin both appearance and light transmittance and was suited for use in alight diffusing plate and the like.

EXAMPLE 6

A sheet having a thickness of 3 mm and a width of 60 cm was continuouslymolded in the same manner as in Example 1 except in the followingrespects: the thickness (Y direction) and the width (X direction) of thecomposite resin flow passage 21 were set at 3 mm and 60 cm,respectively; the slit gap of the outlet of the flow passage 31 was setat 2.6 mm; the pitch p of the groove portions was set at 0.3 mm; and thewidth of the portions Ln and Rn was set at 0.15 mm (P/2).

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape as shown in FIG. 30e. The depressions andprotrusions had a pitch of 0.3 mm, and an h/p ratio of 0.15. The sheetwas excellent in both appearance and light transmittance, showed nouneven light diffusion, and was suited for use in a light diffusingplate, a light guide, and the like.

EXAMPLE 7

A sheet having a thickness of 2.5 mm and a width of 25 cm wascontinuously molded in the same manner as in Example 6 except for thefollowing respects: the thickness (Y direction) and the width (Xdirection) of the composite resin flow passage 21 were set at 5 mm and50 cm, respectively; a die 44 shown in FIG. 18, and FIGS. 19a, 19 b wasarranged at the outlet of the composite resin flow passage 21; the width(X direction) of the outlet was narrowed to ½ (25 cm) of that of theinlet, and the thickness (Y direction) of the outlet was narrowed to½(2.5 mm) of that of the inlet.

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape as shown in FIG. 30a. The depressions andprotrusions had a pitch p of 0.15 mm, and an h/p ratio of 0.25. Thesheet showed optical characteristics as excellent as the sheet inExample 6.

EXAMPLE 8

A composite resin sheet having a thickness of 1.67 mm and a width of16.7 cm was continuously molded in the same manner as in Example 7except that a die shown in FIG. 18, and FIGS. 19a and 19 b was arrangedat the outlet of the composite resin flow passage 21, and that the width(X direction) of the outlet was narrowed to ⅓ (16.7 cm) and thethickness (Y direction) of the outlet was narrowed to ⅓ (1.67 mm) of theinlet.

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape as shown in FIG. 30a. The depressions andprotrusions had a pitch of 0.1 mm, and an h/p ratio of 0.25. The sheetshowed optical characteristics as excellent as the sheet in Example 6.

EXAMPLE 9

A composite resin sheet having a thickness of 3 mm and a width of 60 cmwas continuously molded in the same manner as in Example 6 except thatthe flow passages 41, 42 had a structure in which the positions of theportions Ln and the portions Rn are relatively shifted by p/2 as shownin FIG. 11.

The sheet thus obtained had a smooth surface as a whole, no warpage, anda cross-sectional shape in which the pitch of the upper protrusions andthat of the lower protrusions were relatively shifted by p/2 as shown inFIG. 30h.

EXAMPLE 10

A composite resin sheet having a thickness of 3 mm and a width of 60 cmwas continuously molded in the same manner as in Example 6 except forthe following respects: the thickness (Y direction) of the compositeresin flow passage 21 was set at 3 mm; the thickness (Y direction of theflow passage 31 was set at 0.5 mm; the pitch p of the groove portions ofthe flow passages 41, 42 was set at 0.3 mm; and the width of theportions Ln and Rn was set at 0.1 mm (p/3).

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape shown in FIG. 30f.

EXAMPLE 11

A composite resin sheet having a thickness of 3 mm and a width of 60 cmwas continuously molded in the same manner as in Example 6 except forthe following respects: the thickness (Y direction) of the compositeresin flow passage 21 was set at 3 mm; the thickness (Y direction) ofthe flow passage 31 was set at 2.8 mm; the pitch p of the grooveportions of the flow passages 41, 42 was set at 0.15 mm; and the widthof the portions Ln and Rn was set at 0.075 mm (p/2).

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape shown in FIG. 30e.

EXAMPLE 12

A composite resin sheet having a thickness of 10 mm and a width of 60 cmwas continuously molded in the same manner as in Example 6 except forthe following respects: the thickness (Y direction) of the compositeresin flow passage 21 was set at 10 mm; the thickness (Y direction) ofthe flow passage 31 was set at 9.6 mm; the pitch p of the grooveportions of the flow passages 41, 42 was set at 0.5 mm; and the width ofthe portions Ln and Rn was set at 0.25 mm (p/2).

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape shown in FIG. 30e.

EXAMPLE 13

The same polymethyl methacrylate as in Example 1 was used as the resina, and the same polycarbonate as in Example 1 was used as the resin b.The apparatus shown in FIGS. 1, 2, 20, 21, 22 was used. The grooveportions ΔRn an ΔLn were each set at 1 mm, and the pitch p of the grooveportions was set at 5 mm. The width of the portions Ln and Rn was set at2.5 mm (p/2).

The molding temperature was 260° C. The polymethyl methacrylate wasmelted in a first extruder 1, fed to the die 9 via the extrusion flowpassage 13, and allowed to flow into the composite flow formationportion 22 from the flow passages 41. The polycarbonate was melted atthe same time in a second extruder 2, fed to the die 9 via the extrusionflow passage 14, and allowed to flow into the composite flow formationportion 22 from the flow passages 42. Both resins were allowed to flowinto the composite flow formation portion to form a composite resinflow, which was extruded from the composite flow outlet 23 to give acomposite resin sheet having a thickness of 5 mm and a width of 50 cm.

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape shown in FIG. 31b. The apex angle β was about90°. The depressions and protrusions had a pitch of 5 mm. The sheet wasexcellent in both the appearance and the light transmittance, showed nouneven light diffusion, and was suited for use in a light diffusingplate, and the like.

EXAMPLE 14

A composite resin sheet having a thickness of 5 mm and a width of 50 cmwas continuously molded in the same manner as in Example 13 except thata die 9 having the structure of a composite flow formation portion shownin FIG. 23 was used, and that the height of the flow passages 41 was setat 1 mm.

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape shown in FIG. 24 or FIG. 31c. The apex angle βwas about 90°. The depressions and protrusions had a pitch of 5 mm. Thesheet showed optical characteristics as excellent as the sheet inExample 13.

EXAMPLE 15

A composite resin sheet having a thickness of 3 mm and a width of 50 cmwas continuously molded in the same manner as in Example 13 except forthe following respects: the thickness (Y direction) of the compositeresin flow passage 21 was set at 3 mm; the pitch p of the grooveportions of the flow passages 41, 42 was set at 2 mm; and the width ofthe portions Ln, Rn was set at 1 mm (p/2).

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape shown in FIG. 31b. The apex angle β was about60°. The depressions and protrusions had a pitch of 2 mm. The sheetshowed optical characteristics as excellent as the sheet in Example 13.

EXAMPLE 16

A composite resin sheet having a thickness of 5 mm and a width of 50 cmwas continuously molded in the same manner as in Example 13 except thatthe flow passages were allowed to make an angle of 60° with the YZ planeas shown in FIG. 28.

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape shown in FIG. 31e. The apex angle β was about90°, and the angle α was about 25°. The depressions and protrusions hada pitch of 5 mm. The sheet was excellent in both appearance and lighttransmittance.

EXAMPLE 17

A composite resin sheet having a thickness of 3 mm and a width of 50 cmwas continuously molded in the same manner as in Example 13 except forthe following respects: the thickness (Y direction) of the compositeresin flow passage 21 was set at 3 mm; the pitch p of the grooveportions of the flow passages 41, 42 was set at 0.3 mm; and the width ofthe portions Ln, Rn was set at 0.1 mm (p/3).

The sheet thus obtained had a smooth surface as a whole, no warpage, andthe cross-sectional shape shown in FIG. 31h.

EXAMPLE 18

This is an example of a small surface light source element.

The composite resin sheet obtained in Example 6 was cut to give a lightguide (small surface light source element) for measuring the exitingratio of light having a length of 100 mm in the z direction and a lengthof 300 mm in the x direction. A PET (polyethylene terephthalate) filmcoated with silver by vapor deposition was stuck on the two xy endsurfaces in the longitudinal direction of the light guide with anadhesive, and the back surface of the light guide was covered with a PETfilm coated with silver by vapor deposition using an adhesive tape,whereby a reflecting surface was formed. Moreover, a cold-cathode tubewas placed by the side of one of the yz end surfaces of the light guideso that the longer side of the tube was arranged in the z direction. Thecold-cathode tube and the light guide were covered with a PET filmcoated with silver by vapor deposition.

On the other hand, many columnar prism units each having an apex angleof 63° were formed at a pitch of 50 μm on a PET film with an UV-raycured acrylic resin having a refractive index of 1.53 so that thelongitudinal directions of the columnar prism units were parallel toeach other, whereby a prism sheet was produced.

The prism sheet was placed on the surface of the light guide so that theprism surface faced downwardly and the longitudinal direction of theprism units was in the z direction. The exiting ratio of light of thesmall surface light source element thus prepared was evaluated, and theresults shown in Table 1 were obtained.

The composite resin sheet obtained in Example 6 was cut to give a lightguide having a length of 100 mm in the z direction and a length of 105mm in the x direction, in the same manner as mentioned above. A PET(polyethylene terephthalate) film coated with silver by vapor depositionwas stuck on the two xy end surfaces and one yz end surface of the lightguide with an adhesive. A cold-cathode tube was placed by the side ofthe other yz end surface. A small surface light source element forevaluating the variation of the exiting ratio of light was preparedwhile the other conditions were the same as mentioned above, and theresults as shown in Table 1 were obtained.

EXAMPLES 19 to 21

Small surface light source elements were prepared from the compositeresin sheets obtained in Examples 9, 11 and 17, and their performancewas evaluated. The results shown in Table 1 were obtained.

Comparative Example 1

Two acrylic resin plates each measuring 1.5×100 (z direction)×300 mm (xdirection) were prepared. Columnar prisms were formed (pitch: 0.1 mm,h/p ratio: 0.25) on one surface of one of the resin plates by thermaltransfer with a mold, in parallel with the z direction of the plate. Theother acrylic resin plate was stacked on the plate with its prism-formedsurface faced upward, and bonded thereto to give a light guide havinghollow depressions and protrusions (FIG. 34). A small surface lightsource element for evaluating the exiting ratio of light was prepared inthe same manner as in Example 18, and the performance was evaluated. Theresults as shown in Table 1 were obtained.

Two acrylic resin plates each measuring 1.5 mm×100 mm (z direction)×105mm (x direction) were prepared, and a small surface light source elementfor evaluating the variation was prepared in the same manner asmentioned above. The performance was evaluated, and the results shown inTable 1 were obtained.

The surface light source elements thus obtained each showed a highexiting ratio of light, and a large variation.

Comparative Example 2

Using a mold having a roughened surface formed by blasting a stainlesssteel sheet having a mirror-finished surface with glass beads, theroughened surface was thermally transferred to one major surface of atransparent acrylic plate measuring 3×100 (z direction)×300 mm (xdirection) to give a light guide. Moreover, the roughened surface wasthermally transferred to one major surface of a transparent acrylicresin plate measuring 3×100 (z direction)×105 mm (x direction) to give alight guide. Small surface light source elements were prepared usingthese light guides, in the same manner as in Example 21. The performancewas evaluated, and the results shown in Table 1 were obtained.

The surface light source elements thus obtained each showed a highexiting ratio of light, and a large variation.

Comparative Example 3

The back surface of an acrylic resin plate measuring 3×100 (zdirection)×105 mm (x direction) was screen printed with a spottedpattern using a white paint containing titanium oxide particles. Thedensity of the spots was lowered near the light-incident end surface,and increased with a distance in the x direction from the light-incidentsurface. The resultant acrylic resin plate was used as a light guide,and a small surface light source element was prepared therefrom in thesame manner as in Example 21. The performance of the element wasevaluated, and the results as shown in Table 1 were obtained.

Although the surface light source element thus obtained showed a smallvariation, a spotted pattern was observed through a prism.

EXAMPLE 22

This is an example of a large surface light source element.

The resin sheet obtained in Example 12 was cut to give two light guideseach measuring 10×600 (z direction)×1,000 mm (x direction).

Large surface light source elements for evaluating the exiting ratio oflight and the variation were prepared using the large light guides, inthe same manner as in Example 18. The performance of the light sourceelements was evaluated, and the results shown in Table 1 were obtained.

Comparative Example 4

A large surface light source element as shown in Table 1 was prepared inthe same manner as in Comparative Example 1. The performance of thelight source element was evaluated, and the results shown in Table 1were obtained.

TABLE 1 Optical Shape of depressions and characteristics protrusionsExiting Shape of Size of ratio depressions Pitch light guide of Resinand protru- p h (height) z × x × y Variation light Ex. No. sheet sions(mm) /p (pitch) (mm) (R%) (%) Ex. 18 Ex. 6 FIG. 30e 0.3 0.15 100 105 319 1.91 Ex. 19 Ex. 9 FIG. 30h 0.3 0.15 100 105 3 14 1.67 Ex. 20 Ex. 11FIG. 30e 0.15 0.15 100 105 3 18 1.89 Ex. 21 Ex. 17 FIG. 31h 0.3 0.36 100105 3 15 1.71 Comp. Ex. 1 hollow 0.3 0.25 100 105 3 182 6.83 FIG. 34Comp. Ex. 2 surface-sand 100 105 3 83 4.62 blasted Comp. Ex. 3dot-printed 100 105 3 12 — Ex. 22 Ex. 12 FIG. 30e 0.5 0.15 600 1000 10155 1.87 Comp. Ex. 4 hollow 0.5 0.25 600 1000 10 800 7.02 FIG. 34

EXAMPLE 23

This is an embodiment of a laminate.

A composite resin sheet having a thickness of 3 mm and a width of 50 cmwas prepared in the same manner as in Example 1 except for the followingrespects: the pitch p of the groove portions was set at 3 mm; the widthof the portions Ln, Rn was set at 1.5 mm (p/2); and a polymethylmethacrylate (trade name of Acrypet VH, manufactured by Mitsubishi RayonCo., Ltd.) was used as the resin layer a.

The shape of the cross-sectional depressions and protrusions of thesheet thus obtained was sawtooth-like as shown in FIG. 31b, and thedepressions and protrusions had a pitch p of 3 mm, a height h of 1.5 mm,an angle α of 450° and an apex angle β of 90°.

Two of the resin sheets were laminated with methylene chloride used asan adhesive so that the x direction of one of the sheets crossed the xdirection of the other at an angle of 90° and both resin layers B facedthe inner side of the laminate to give a resin sheet laminate having athickness of 6 mm, a longitudinal length of 50 cm and a transverselength of 50 cm.

The laminate thus obtained had a grid-like pattern having a deepappearance and a three-dimensional appearance, exhibited an excellentlight transmittance and light divisibility, and had an appearance ofhigh grade the color tone of which the appearance changed depending on aviewing angle due to a reflection effect, a diffusion effect, and aneffect of light at the interface of the depressions and the protrusionswithin the laminate.

EXAMPLE 24

Two of the resin sheets (FIG. 30d) obtained in Example 2 were laminatedwith methylene chloride as an adhesive so that the x direction of one ofthe sheets crossed the x direction of the other sheet at an angle of 90°to give a resin sheet laminate having a thickness of 6 mm, alongitudinal length of 50 cm and a transverse length of 50 cm.

The laminate thus obtained showed a performance equivalent to that ofthe laminate in Example 23.

EXAMPLE 25

A resin sheet laminate was prepared in the same manner as described inExample 24 from two of the resin sheets (FIG. 30h) obtained in Example9.

The laminate thus obtained showed a performance equivalent to that ofthe laminate in Example 23.

Industrial Applicability

The resin sheet of the present invention is applicable to variousobjects and uses such as a light diffusible sheet suitable for anilluminator cover, a lighting window, a building material, a trafficsign, a sign board, a liquid crystal display device, etc., and anartistic design sheet having a deep appearance and/or athree-dimensional appearance, and is, therefore, extremely useful inindustry. Furthermore, a surface light source element can be obtained byusing the resin sheet as a light guide, and a useful laminate can beobtained by laminating such resin sheets.

What is claimed is:
 1. A surface light source element comprising: aresin sheet having a laminate structure in which a transparent resinlayer C is sandwiched between and adjacent each of a transparent resinlayer A and a transparent resin layer B, and a smooth an outer surface,any two adjacent resin layers of the three resin layers havingrefractive indexes which differ from each other, in a cross-sectionrepresented by an xy plane wherein y is a thickness direction of the aresin sheet, and x is a width direction thereof, at least one of twointerfaces formed between the resin layers A and C and between the resinlayers B and C having an uneven shape formed by repeated pluraldepressions and protrusions, as a light guide, a reflective materialarranged on a lower surface of the light guide, a light source placed atleast on one end surface (yz plane) in an x direction of the lightguide, and a light-deflecting sheet placed on an upper surface of thelight guide and having a function of changing a direction of light whichis allowed to exit from a surface thereof to a normal direction thereof.2. The surface light source element according to claim 1, wherein theuneven shape at an interface of resin layers in an xy cross-section ofthe resin sheet has a pitch p of 50 to 600 μm.
 3. The surface lightsource element according to claim 2, wherein the pitch p of the unevenshape is 50 to 200 μm.
 4. A surface light source element comprising: aresin sheet having a laminate structure of a transparent resin layer Aadjacent a transparent resin layer B, and an outer surface, the adjacentresin layers having reflective indexes which differ from each other, ina cross-section represented by an xy plane wherein y is a thicknessdirection of the resin sheet, and x is a width direction thereof, aninterface formed between the resin layers A and B and having an unevenshape formed by repeated plural depressions and protrusions, as a lightguide, a reflective material arranged on a lower surface of the lightguide, a light source placed at least on one end surface (yz plane) inan x direction of the light guide, and a light-deflecting sheet placedon an upper surface thereof and having a function of changing adirection of light which is allowed to exit from a surface thereof to anormal direction thereof.
 5. The surface light source element accordingto claim 4, wherein the uneven shape at an interface of resin layers inan xy cross-section of the resin sheet has a pitch p of 50 to 600 μm. 6.The surface light source element according to claim 5, wherein the pitchp of the uneven shape is 50 to 200 μm.